Plastic syringes are commonly used for medical treatment, surgery and scientific research. Due to the invasive nature of these articles, which are most often used to pierce the skin of a patient, sterility and durability are of prime concern.
Radiation sterilization of syringes, often the preferred sterilization method, is known in the art. (See U.S. Pat. No. 3,315,802). Packaging for radiation sterilized syringes is generally light, pliable, and heat sealable. Both gas permeable and gas impermeable packaging may be used. Packaging materials commonly used include plastic films, paper adhesives and plastic/foil laminates. (See U.S. Pat. Nos. 3,315,802 and 2,813,623). Examples of suitable plastics are polyethylene and polyvinylchloride. Suitable foils include those produced from aluminum in combination with polymers.
Radiation sterilized syringes tend to become brittle, and lose durability with aging. Additionally, substantial yellow discoloring occurs. This discoloring is unpleasant to both patients and medical personnel since it lends a "used" appearance to the syringe that can result in a loss of patient confidence that syringes used on them are new and clean. Due to the possibility of contracting dangerous or even deadly disorders from re-used syringe needles, syringes that become noticeably yellow are sometimes unacceptable for their intended use. Also, because these articles increase in brittleness with age, the lengthy storage time which is common prior to use mandates a sterilization process which does not cause substantial brittleness, so that the articles will not crack or fall apart during use. The brittleness problem is compounded by the common practice of autoclaving prior to use to re-sterilize the outside of the container, to meet with hospital sterility requirements.
Thus, due to the requirement of sterile and durable medical articles which are not discolored, there exists a need for a radiation sterilization method that does not cause substantial yellowing or increased brittleness.